DESCRIPTION: (Taken from the abstract). Infection of cats with the feline immunodeficiency virus (FIV) produces an immunodeficiency syndrome with pathogenesis very similar to that observed in HIV. FIV shares several genetic similarities with HIV and therefore provides an animal model for evaluating viral determinants of pathogenesis. Critical for the design of an efficacious lentivirus vaccine is the identification of viral antigens that are essential for inducing protective immune responses; at the same time it is necessary to elucidate and eliminate viral functions that may lead to immune systems dyregulation. The proposed experiments are based on the hypothesis that infection of cats with mutant FIV clones by proviral DNA injections will be a means to achieve protective immunity. Three specific aims are proposed: Specific Aim 1: To evaluate viral replication, distribution and immunopathological abnormalities during the primary stage and later stages of infection in specific tissue and cell populations harvested from cats infected with infectious FIV mutant viruses delivered by intramuscular injection of proviral DNA. Specific Aim 2: To analyze virus specific cytotoxic T-cell responses, neutralizing antibody avidity in cats inoculated with infectious mutant proviral DNA. Specific Aim 3: To test for protective immunity in cats inoculated with infectious mutant proviral DNA by challenging with pathogenic biological isolates of FIV.